1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method. More specifically, the present invention relates to an electrophotographic type or electrostatic type image forming apparatus, such as a copier, facsimile, printer, and so-called digital multifunction peripheral, and an image forming method, and more particularly to a determination as to whether an image adjusting operation is executed or not in a color image forming apparatus.
2. Description of the Related Art
There have been known color image forming apparatuses that print and output the result, which has been subject to various image forming processes, based upon externally received image data or image data obtained by reading a document. Of these color image forming apparatuses, a so-called multifunction peripheral (MFP) having not only a basic function such as a printer function, a scanner function, a facsimile function, a copy function, etc., but also various functions utilizing a network communication becomes widespread.
Since, in a color image forming apparatus, an image quality varies depending upon the difference in the environment where the apparatus is used, such as a temperature or humidity, or a printed document, an image adjusting operation (also referred to as a process control or image correction) is periodically executed.
There has been known a color image forming apparatus that avoids a control operation of image forming operations by which an image forming condition greatly varies, and executes a first control and a second control in order to prevent a color phase of a color image from varying (see, for example, Japanese Unexamined Patent Application No. 2006-259442). In this apparatus, the first control controls a change value of an exposure amount so as to fall within a predetermined range, while in the second control, correction values of exposure amounts of image exposure means corresponding to plural colors are calculated respectively, and the exposure amount of exposure means is controlled based upon the calculated values.
Although the periodic execution of the image adjusting operation is excellent in stably maintaining a printed image, this operation is very unfavorable for a user who has to be in a hurry, since this adjusting operation needs several ten seconds to several minutes. For the image adjustment, a pattern for the image adjustment is formed on a photoconductor by using a developer (toner), so that some amounts of developer (toner) are consumed. Therefore, the apparatus has a drawback that the amount of developer (toner) that can be used for an actual print job is reduced.
In view of this, a color image forming apparatus performing a high image density correction and a halftone density correction has been proposed in which the previous result and the result this time in the high image density correction are compared, and only when the difference becomes not less than a difference reference value set beforehand, the halftone density correction is executed (see, for example, Japanese Unexamined Patent Application No. 2001-13748).
A color image forming apparatus also has a function of forming an image in black and white. A color image forming apparatus generally includes image forming sections for forming images of color components of yellow (Y), magenta (M), cyan (C), and black (K), wherein the images of Y, M, C, and K formed at the respective image forming sections are superimposed. On the contrary, it is unnecessary to form images other than the K color component in a black-and-white image, so that the image forming sections of Y, M, and C are not operated. Accordingly, the image adjustment for the Y, M, and C does not have to be performed for the black-and-white printing. Since the image forming sections of Y, M, and C are not operated, the print cost for the black-and-white image is cheaper than the print cost for the color image. Therefore, the charging for a user involved with the printing is made independently for a color printing and a black-and-white printing.
Therefore, a user who carries out a black-and-white printing in most cases cannot allow extra time and cost caused by the image adjustment for Y, M, and C that is executed when a color printing is not performed. On the other hand, the ratio of the black-and-white printing and the color printing is different by each user. Further, the ratio may vary depending upon a period even by the same user.